1. Field of the Invention
The present invention relates to an observation device, an ultraviolet microscope, and an observation method which observe a specimen by light in the ultraviolet region or the deep ultraviolet region.
2. Description of Related Art
An ultraviolet microscope is known from the prior art which observes a specimen by light in the ultraviolet region or the deep ultraviolet region (light whose wavelength is 356 nm, 266 nm, 248 nm or the like will generally be termed “ultraviolet light”). Because ultraviolet microscopes have high resolving power as compared with optical microscopes which utilize visible light, they are nowadays employed in fields in which miniaturization is progressing.
In this connection, in the semiconductor field, the miniaturization of patterns on wafers has progressed conspicuously along with the great increase in the integration of semiconductor elements. In recent years, the line width of patterns has been approximately from 0.13 μm to 0.24 μm. Since a pattern which has been miniaturized to such an extent cannot be observed with an optical microscope which utilizes visible light, the use of ultraviolet microscopes is being investigated in the semiconductor field as well.
However, since with an ultraviolet microscope according to the prior art the specimen is observed in air in the same way as with a conventional optical microscope which utilizes visible light, therefore, as shown in FIG. 9, oxygen in the air 93 which is present between the specimen 91 and the objective lens 92 is converted into ozone by the ultraviolet light LUV, and furthermore a portion of the ozone becomes oxygen plasma (active oxygen), and this causes undesirable damage to the surface of the specimen 91.
For example, in the case of a specimen 91 which consists of a resist pattern formed upon a wafer, such as is used in a semiconductor manufacturing process, the surface of the resist pattern can easily be removed by the oxygen plasma (the active oxygen) in the air 93, which is undesirable. In other words, dissociation reaction of the resist molecules upon the surface of the resist pattern takes place due to the oxygen plasma (the active oxygen), and the dissociated resist molecules which have been converted into low molecular weight are undesirably evaporated or transpired due to combination with the oxygen in the air 93.
Furthermore, if the wavelength of the ultraviolet light LUV for the ultraviolet microscope is close to the exposure light wavelength when forming the resist pattern (which generally nowadays is 248 nm), when observing with the ultraviolet light LUV, sometimes the resist pattern is undesirably exposed for a second time. Due to this, dissociation reaction of the resist molecules takes place in the areas which are irradiated with the ultraviolet light LUV, and this causes damage in the same manner as described above.